1. Field of the Invention
The present invention relates to an air bag apparatus which is attached to a steering wheel.
2. Description of the Related Art
Recently, a vehicle operator's seat is equipped with, in general, an air bag apparatus serving as a passive safety auxiliary device (SRS: supplemental restraint system). FIG. 11 illustrates the structure of such vehicle operator's seat SRS air bag. The entire air bag apparatus is integrally assembled to a steering wheel 14 which is secured to the distal end portion of a steering main shaft 12 in a steering column 10.
As a result, in the steering wheel 14, a boss portion 18 of the steering wheel 14 is connected to a serration portion 16 at the distal end of the steering main shaft 12. Further, the boss portion 18 is connected to a conical inclined surface of the steering main shaft 12 so that the boss portion 18 is not inserted in the axial direction thereof. The boss portion 18 is secured by a bolt 20 so that the boss portion 18 is not removed from the end portion of the steering main shaft 12. An air bag apparatus main body 26 is provided within a concave space surrounded by the boss portion 18, a spoke portion 22, and a wheel portion 24 of the steering wheel 14. The air bag apparatus main body 26 is covered by a steering wheel pad 28 and a lower cover 30.
In the air bag apparatus main body 26, as gas is rapidly injected from an inflator 34 into a bag body 32 so as to inflate the bag body 32, the steering wheel pad 28 is broken away and the bag body 32 is unfolded in a predetermined state. When large acceleration is applied to a vehicle, an ignition device of the inflator 34 is energized due to the designation of a central control unit which has detected the acceleration, such that gas generating agent is combusted, a large amount of gas is generated, and the bag body 32 is unfolded. In the air bag apparatus main body 26 which performs electrical ignition and control in this way, it is necessary to connect electrically the air bag apparatus main body 26 and the central control unit disposed at the vehicle body side. As a result, an unillustrated roll connector is disposed at a rotating portion between a steering column 10, which is fixed to the vehicle body, and the steering wheel 14, which is rotated with respect to the steering column 10. The central control unit and the inflator 34 are electrically connected via the roll connector so that the inflator 34 is energized highly reliably.
When the air bag apparatus main body 26 is attached to the steering wheel 14 in this way, it is necessary to have a large space for attaching the large roll connector at the rotating portion between the steering column 10 and the steering wheel 14. Therefore, the portion at which the roll connector is disposed is increased, and since the expensive roll connector is used, the product becomes expensive.
Moreover, there is need to increase the concave space surrounded by the boss portion 18, the spoke portion 22, and the wheel portion 24 of the steering wheel 14 so as to accommodate the bag body 32 and the inflator 34 simultaneously. Accordingly, the design of entire steering wheel 14 is restricted. Further, because the bag body 32 and the heavily-weighted inflator 34 are integrally attached to the steering wheel 14, the mass of the rotating portion of the steering wheel 14 increases. Thus, it is difficult to design the steering wheel 14 for improving the vibration characteristics thereof at the time of running of the vehicle.